Compass system



C. E; HURLBURT COMPASS SYSTEM July 24, 1956 Filed April 17 1951INVENTOR. C HA PLES E. HURL BURT BITOR/VEY United States Patent COMPASSSYSTEM Charles E. Hurlburt, Teaneck, N. J., assignor to Bendix AviationCorporation, Teterboro, N. J., a corporation of Delaware ApplicationApril 17, 1951, Serial No. 221,447

3 Claims. (Cl. 33-222) The invention relates generally to datatransmission systems, and more particularly to compass systems whereindirection indications are provided remote from a transmitter sensitiveto the earths magnetic field, and which may comprise a permanent magnetand a flux valve.

The flux valve, as referred to in the present specification and claims,is a device which interacts with a magnetic field and provides anelectrical signal of a phase and magnitude determined by the position ofthe flux valve in the magnetic field. I

One object of the present invention is to provide a compass system foruse in aircraft having a flux valve responsive to the magnetic fieldprovided by a permanent magnet oriented angularly by the earths magneticfield and positioned in a plane parallel to the plane of the fiux valveand coaxial with the flux valve irrespective of the attitude of thecraft in which the'compass system is mounted.

Another object is to provide a compass system in which the direction ofthe earths magnetic field is indicated remotely by an indicator operatedby a servo system utilizing a single thyratron tube and responsive tothe flux valve.

The invention contemplates a compass system having a flux valvesupported by a pair of gimbals rotatable about mutually perpendicularaxes and a permanent magnet associated therewith and mounted forrotation about the axis of the flux valve and positioned in a planeparallel to the plane of the flux valve. In a preferred embodiment, themagnet is supported at a point coinciding with the point of intersectionof the gimbal axes. The magnet and flux valve may be immersed in aviscous fluid to damp their movements.

The compass system preferably includes a servo having driving means foroperating a pointer and connected across an alternating power source anddriven in one direction thereby when the signal from the flux valve asdetermined by the position of the flux valve in the magnetic field is ofone phase. When the flux valve is positioned in the magnetic field sothat the signal induced therein is of the opposite phase a thyratrontube fires and energizes the driving means for rotation in the oppositedirection in opposition to the power source.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingwherein one embodiment of the invention is illustrated. It is to beexpressly understood, however, that the drawing is for the purposes ofillustration and description only, and is not to be construed asdefining the limits of the invention.

The single figure of the drawing shows a compass systern constructedaccording to the invention. The transmitter is shown in perspective andthe electrical components are shown schematically.

Referring now to the drawing for a more detailed description of thenovel compass system of the present in- Patented July 24, 1956 vention,the compass system is shown as comprising a transmitter including a fluxvalve 1 substantially of the kind shown and described in applicationSerial No. 151,402, filed March 23, 1950, by John F. Emerson, now PatentNo. 2,710,942 issued June 14, 1955, and assigned to the same assignee asthe present application. The flux valve includes a plurality of coremembers 3 arranged on a platform 4 in the form of an equilateraltriangle and each core member has a primary winding 5 and a secondarywinding 7 wound thereon. The primary windings are connected in serieswith one another through a half-wave rectifier 9 to an alternatingcurrent source S and the secondary windings are connected together in Yrelationship and each has induced threin an alternating current voltageof the same frequency as the alternating current source, the phase senseand magnitude being determined by the position of the flux valverelative to the magnetic field.

The flux valve is pendulously suspended in the craft by a pair ofgimbals 11, 13 rotatable about mutually perpendicular axes XX and YY sothat the flux valve is positioned in a horizontal plane irrespective ofthe attitude of the craft. The platform of the flux valve may besupported rigidly by a plurality of straps 14 from gimbal 11.

A pair of permanent magnets 15 are mounted on a compass card 16supported by pivot 17 secured by rods 18 to a housing 21 enclosing thetransmitter. The compass card is supported by pivot 17 from a point 19at the intersection of axes XX and YY so that the compass card mayrotate freely in azimuth relative to the flux valve and so that themagnets are aligned with the horizontal component of the earths magneticfield. The compass card is pendulous also so that it pivots about point19 to position the magnets substantially in a horizontal planeirrespective of the attitude of the craft mounting the compass system.With the suspension described, if the flux valve swings about point 19in response to acceleration of the craft, compass card 16 pivots alsoand is always coaxial with the flux valve and magnets 15 are always in aplane parallel to the plane of the flux valve.

The magnet and flux valve are enclosed in housing 21 and the housingpreferably is filled with viscous fluid to damp movement of the compasscard and flux valve. The compass card preferably has an inclinedcircumferential face 22 to resist pivotal movement in the fluid.

With the arrangement described, a signal of greater magnitude is inducedin the secondary windings of the flux valve by the uni-directionalpulsating current in the presence of the field of the permanent magnet15 than would be induced in the flux valve in the presence of therelatively weak earths magnetic field alone.

A receiver inductive device 27 has a three-circuit stator winding 28connected back-to-back to the secondary windings of the flux valve and asingle circuit rotor winding 29 inductively coupled thereto andconnected to a broadly tuned circuit 30, including an inductance 31, acapacitance 33 and a matching transformer 35. The tuned circuit convertsthe irregular wave form of signal substantially to a sine wave.

The sine wave from tuned circuit 30 is applied to a control circuit 37preferably of the kind shown and described in applicants copendingapplication Serial No. 220,034, filed April 9, 1951, and assigned to thesame assignee as the present application. The control circuit preferablycomprises a single thyratron tube 39 having its control grid 41connected to one end of secondary winding 43 of transformer 35. Cathode44 and screen grid 45 of thyratron tube 39 are connected together and tothe other end of secondary winding 43 of transformer 35.

A two-phas reversible motor 46 has a rotor 47 drivably connected to adirection indicator 48 and to rotor 29 of inductive device 27. The motoralso has a pair of field windings 49., .51 connected through a phasingcondenser .53 to alternatingcurrent source S. Motor .46 also has anauxiliary field .Winding 55 connected to plate 57 of thyratron tube .39.

The primaryand secondary windings of the flux valve, the stator :androtor windings of the inductive device, transformer 35, cathode .44 ofthyratron tube 39 and field windings 49, 51 .of motor 46 are connectedby a common lead 59 to one side of alternating current source 5.

When the error signal between the flux valve and inductive device 27 isopposite in phase to the voltage from source S impressed .on plate 57.of thyratron tube 39 through auxiliary motor winding .55, thyratrontube .39 will not fire and windings 49, 51 exert a torque on rotor 47 todrive the rotor in one direction and rotate pointer 43 and rotor winding29 of inductive device 27 toward null position. 1

When the error signal between the flux valve and inductive device 27 isin phase with the voltage from source S impressed on plate 57 of.thyratron tube 39 through auxiliary motor winding '55, thyratron tube39 fires and energizes auxiliary motor winding 55. The torque exerted byauxiliary motor winding 55 and winding 49 on rotor 47 is greater thanand opposite to the torque exerted by motor windings 51, .49 on rotor 47and the motor drives pointer 48 and rotor winding 29 in the oppositedirection toward null position.

Motor 46 drives rotor 29 of receiver inductive device 27 towardelectrical coincidence with the transmitter from either side ofcoincidence and equilibrium is attained when thyratron tube39 passesplate current so that the torque developed by auxiliary motor winding 55and winding 49 is equal and opposite to the torque developed by motorwindings 51, 49. This is accomplished by a small phase inversion inreceiver 27 of the grid voltage relative to the plate voltage whichcauses thyratron tube 39 to fire fora portion of each cycle.

By exciting the flux valve with a half-wave rectified voltage from analternating current source, the field windings of the motor may beenergized by the same alternating current source Without doubling thefrequency. Also, by having the flux valve detect the relatively strongfield of the permanent magnet instead of the earths relatively weakfield alone, the errors which would be present if half-wave rectifiedcurrent were used to energize the flux valve are avoided.

With the magnet and flux valve suspension described herein, the magnetand flux valve are pendulously supported for rotation about a singlepoint and remain parallel and coaxial irrespective of the attitude ofthe craft on which the compass system is mounted, and this reduces tilterror to a negligible amount.

While the system is described as being used to indicate direction, itshould be understood that motor 46 may be used to operate a controlsurface of an aircraft, such as a rudder or aileron, to maintain thecraft on a fixed course.

Although but on embodiment of the invention has been illustrated anddescribed in detail, it is to be expressely understood that theinvention is not limited thereto. Various changes can be made in thedesign and arrangement of the parts without departing from the spiritand scope of the invention as the same will now be understood by thoseskilled in the art.

What is claimed is:

l. Ina compass system for a craft, a flux valve, a pendulous support forsaid flux valve providing for movement of said flux valve about mutuallyperpendicular axes, a permanent magnet associated with said flux valve,and means separate from said pendulous support for suspending saidpermanent magnet at substantially the point of intersection of saidmutually perpendicular axes for rotation about the flux valve axis andfor maintaining said permanent magnet in a plane parallel to the planeof said flux valve irrespective of the attitude of the craft.

2. Structure as described in claim 1 in which the permanent magnet andflux valve are immersed in a viscous fluid for damping their movements.

3. Structure as described in claim 1 in which the permanent magnet ispendulous and is supported by a pivot.

References Cited in the file of this patent UNITED STATES PATENTS478,017 Oliver June 28, 1892 2,026,919 Stright Jan. 7, 1936 2,308,566Noxon Jan. 1-9, 1943 2,349,963 Harrison May 30, 1944 2,361,433 StuartOct. 31, 1944 2,373,096 Bonell Apr. 10, 1945 FOREIGN PATENTS 507,889Great Britain June 22, 1939

